A two-rotor continuous mixer of plastic materials has a mixer barrel for housing a mixing chamber having an in-feed location near an upstream end of the mixing chamber and an outlet near a downstream end of this chamber. Ingredients for plastic materials to be mixed are introduced into the in-feed location. Continuous turning of the two rotors within the mixing chamber causes the plastic materials to move downstream in the mixing chamber from the in-feed to the outlet. Resulting mixed molten plastic materials flow out of the outlet. Considerable amounts of heat are generated around the two rotors continuously turning in their mixing of plastic materials within the mixing chamber. The heat being generated is more severe near the downstream end of the mixing chamber as compared with the upstream end.
Each of the two rotors in prior art continuous mixers is a one-piece steel member of elongated configuration having a drive journal for the upstream end of the rotor and a driven journal for the downstream end of the rotor. The drive and driven journals of the two rotors are rotatably supported in drive and driven journal bearing assemblies, respectively, located upstream and downstream relative to the mixing chamber.
In the prior art, in order to lubricate the journal bearing assemblies while at the same time counteracting the severe heating effects being imposed upon the main rotor section of each one-piece rotor in the mixing chamber, oil traditionally has been circulated for lubricating the journal bearing assemblies. This circulating oil has been cooled, usually by pumping the oil through heat exchangers cooled with circulating water. The overall results of traditional cooled-oil circulation systems with their oil pumps, filters, oil reservoirs or sumps, oil lines and associated interconnections and hardware, heat interchangers with plumbing for circulating cooling water, mounting framework, electrical conduits, shut-off switches and circuit breakers, etc. are bulky, expensive lubricating systems, which consume electrical power each day for running oil pumps and which often involve some unpleasant ambient noise caused by continuous operation of their oil pumps and which must be maintained.